When it comes to lamellar surgery, a bevy of options

April 18, 2015

With the influx of numerous endothelial keratoplasty procedures, only 15% of corneal transplants last year were penetrating keratoplasty (PK), said Donald T.H. Tan, MD, Singapore.

San Diego-With the influx of numerous endothelial keratoplasty procedures, only 15% of corneal transplants last year were penetrating keratoplasty (PK), said Donald T.H. Tan, MD, Singapore.

“We need to seek alternative technologies for lamellar dissection,” he said. “It’s not just the art-we need to go back to the technology.”

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Dr. Tan presented the Binkhorst Lecture during the opening general session at the 2015 meeting of the American Society of Cataract and Refractive Surgery.

“This is a truly tremendous honor and privilege,” Dr. Tan said, who dedicated the talk to the “giants and champions who are changing the field of corneal transplantation.”

To that end, Dr. Tan is introducing for the first time at this conference a patent-pending piezo-electric corneal knife.

“This is already in wide use in cataract surgery,” he said.

The high-frequency ultrasound fragments the cataract and features a blunt dissector. Using that technology, the vibration will separate the corneal layers so that the second dissected layer is only 30 μm.

The Singapore Corneal Transplant Study-which comprised 2,300 transplants followed for the more than 12 years-found that after the first year, graft survival was about the same for PK, deep anterior lamellar keratoplasty (DALK), and Descemet’s stripping automated endothelial keratoplasty (DSAEK). However, by years 3 and 5, DALK started to show better longevity.

Next: Why are more countries not adopting these procedures?

 

“At year 5, there is a 93% survival rate for DALK; 77% for DSAEK; and 71% for PK graft survival,” Dr. Tan said.

When it comes to regions of the world that have rapidly embraced endothelial keratoplasty procedures, Sweden is leading the world, followed closely by the United States and Singapore.

“Why are more countries not adopting these procedures?” he asked. “First, there has to be confidence in the superiority of the procedure and shorter learning curves. Next, it needs to make sense financially.”

He attributes the increasing popularity of DSAEK to eye banks’ abilities to cut tissue more precisely.

“The economics of EK procedures could be better, but it ain’t that bad,” he joked. In the United States, EK procedures now account for 56% of all corneal transplants.

“Conundrums and challenges” remain, Dr. Tan said, including determining how to maneuver an 8- to 9-mm donor through a 4-mm incision, and how to improve endothelial cell loss rates. Currently, “cell loss ranges from 20% to 60%. The 1-year cell loss for DSEK is 38%, and for PK, 20%.”

The Tan EndoGlide (named after Dr. Tan) has helped normalize the cell loss rate to 15%, and Dr. Tan credits Massimo Busin, MD, with “showing us how to pull donor tissue in to maintain maximal control and protect the endothelium.”

For patients with failed PKs, a second PK graft is not nearly as successful as performing DSAEK over the initial PK, he said.

The latest of the EK procedures, Descemet’s membrane endothelial keratoplasty (DMEK), “is probably anatomically the best of the EK procedures, but it is the most challenging,” Dr. Tan said.

Next: DALK is 'much better' than PK

 

Corneal transplant surgery “needs to be a low-tech procedure,” Dr. Tan said, noting at its most simplistic there should only be an IOL shooter, balanced salt solution, and air.

Anterior lamellar keratoplasty procedures are “more art than science,” Dr. Tan said.  Singapore and Brazil lead the world in adaptation, whereas the United States has a 2% adoption rate.

“Why? It’s not at the tipping point yet in many countries,” he said. “There’s no technology-the microkeratome can’t cut deep enough and the femto produces poor cut profiles. It’s not economically viable.”

However, DALK is “much better” than PK outcomes in the Singapore transplant study. Some pearls-using Anwar’s big bubble technique is more successful and predictable “if there is manual removal of the top stoma layer before you inject the big bubble,” he said.

How can the surgery be made easier?

“There are only two blunt instruments needed for deep dissection-a Sinskey hook and a DALK marginal dissector,” he said.

The field of corneal transplantation is rapidly evolving, he summarized.

“EK is the gold standard for endothelial dysfunction, but needs to continue to improve,” Dr. Tan said. “Technology advances are still needed and still welcomed.”

The ASCRS Binkhorst Lecture and medal is presented each year in honor of Cornelius D. Binkhorst, MD, to an individual who has made outstanding contributions to the understanding and practice of anterior segment surgery.